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The number of kea to have died in Mt Aspiring National Park’s Matukituki Valley west of Wanaka could be more than the six found so far.
The six dead birds, recovered after an aerial drop of 1080 poison targeted predators last month, were all wearing transmitters fitted by the Kea Conservation Trust.
Trust chairwoman Tamsin Orr-Walker said yesterday she was "hugely saddened".
"Obviously its pretty tragic having birds you have been working with end up in this situation."
She pointed out the six were "just a monitored sample" of the kea in the valley.
"So yes, more kea are likely to have died."
The Department of Conservation carried out the 1080 drop and expects to have post-mortem and toxicology results determining the cause of the deaths by the end of the week.
Threats director Amber Bill said Doc was "confident" predator control operations benefited kea populations but "it’s upsetting to lose six birds".
The dead kea were all known as "hut birds" — those that interacted with and were fed by people.
Ms Bill said Doc was concerned the kea might have been exposed to human food making them "potentially more vulnerable to picking up 1080 cereal baits".
Ms Orr-Walker said her trust’s field staff knew from experience kea being fed by people led to them interfering with traps and bait stations "and picking up toxic bait".
"It’s a huge part of the problem."
Ms Bill said Doc had carried out research on 222 monitored kea through 19 aerial 1080 operations at 12 South Island sites.
Overall, there have been 24 kea deaths with only three at remote sites.
"This research shows the risk of 1080 to kea in remote areas is low but increases markedly with birds that have learnt to scavenge for human food."
The Matukituki 1080 drop had followed Doc’s code of practice to "mitigate risks to kea", she said.
It followed the biggest "mast" — or beech tree seed drop — for 40 years.
That had fuelled "rodent plagues", producing "a spike in stoat numbers, and posing a serious threat to ground-nesting kea and other native wildlife," Ms Bill said.
"Research also shows that kea populations are better off when aerial 1080 is used to control rats and stoats, with increased survival and nesting success," she said.